The present invention relates to a soldering wire, constituted by a core of powder and a tubular metallic member surrounding the core, to be used for automatic or semi-automatic soldering, with or without a protective gas, as well as to a method of manufacturing such a soldering wire.
It is known in the art to use a soldering wire or a wire for hard surfacing which is composed of an outer metallic sheath and a core of powder surrounded by this sheath. The cylindrical or polygonal sheath is usually formed from a band of steel, which may or may not be alloyed, or from another metal which contributes to the soldering. The core of the soldering wire, which constitutes usually 10 to 50% of the total weight of the wire is composed of a pulverulent mixture usually comprising a plurality of the following components in different combinations in accordance with the work to be performed and in accordance with the conditions prevailing during the soldering. Such components may include a slag forming material of an oxide base and/or carbonates of alkaline earth metal, a flux--forming material of fluoride base and/or alkaline halogenides or alkaline earth metal, deoxidizing and denitrating metals such as Al, Mg, Si, Ti, Mn and different alloys of such metal, one or a plurality of products for stabilization of the soldering arc, for example a titanium base of calcium or potassium, a support material of ferric base, of ferro alloys or other metals and alloys to form the desired soldering composition. Other mineral and metallic products may be included in the composition of the powder, but since the specific composition of the powder does not form part of the present invention, the above enumeration of such compositions is considered to be sufficient.
A process of fabricating such soldering wires with a core of powder is also known in the art which consists to transform a continuous metallic band into a channel, to introduce the pulverulent mixture in such a channel, to form the channel by one or a plurality of rolling operations or drawing operations by means of a drawing die into a tubular member enclosing the powder, and to close the metallic member by forming a weld seam connecting the longitudinal edges before proceeding with the final drawing operation to impart to the thus formed soldering wire the desired diameter.
This known process of fabrication has considerable drawbacks in that the powder tends to disperse and to stick to the bent borders of the channel during closure of the same and to stick especially to these borders during connecting the borders of the channel by soldering or welding. This will result in a joint of the borders by soldering or welding of such poor quality that the final transformation of the filled tube by drawing is rendered very difficult and the diameter of the thus-formed soldering wire can therefore be reduced by drawing only to a small extent.
Various solutions to overcome this drawback are known in the art. A first solution consists to reduce the amount of powder which is fed into the channel. This of course leads to a corresponding increase of the ratio of solid metal to the powder in the soldering wire thus obtained. Furthermore, this solution necessarily leads to difficulties in maintaining the homogeneity and uniform distribution of the powder during the fabrication and the transformation of the tubular wire. The possibility to use such a soldering wire having a disadvantageous ratio of powder to metal and an irregular quality and evidently very limited. Another solution, which likewise will only partially solve the above pointed out problem, consists to submit the powder distributed in the channel to an equalization and compacting prior to closing the tube blank. A further solution which entails a complication in the technique of preparing the powder and the introduction thereof into the channel consists to mix the powder with a binder and to extrude the thus formed plastic mass in form of a continuous, preformed strand into the channel. This last-mentioned solution is burdensome and does not lend itself to competitive mass fabrication. Thus, all of the above-mentioned solutions have not found an industrial application for manufacturing tubular soldering wires with a soldered or welded joint.